Method of and means for polishing metal surfaces



Patented Aug. 28, 1928.

UNIZTTED STATES EN FFICE. I

'WILLIAMI; WEBER, orflcnrcaeo rtm nors METHOD. OE'AND' MEANS'FOR POLISHING METAL" SURFACES.

No Drawing.

pose of'disclosing the invention reference' will bemade to what is at'present considered apieferred means for and method of accomplishlng the result and to a motor or generlfisatorcommutator for illustrating the method and the useof means for carrying out the process.

It is very desirable to provide afhardand highly polished:v running surface 1 on com mu tators, collector rings and the like of a dynamo-electric machine so that thebrushes riding on such surface will not wearitfexcessively while making good'electricalcon tact. No matter how well polished and otherwise perfect a commut-ating or collector ring surface may-be, when the motor or the like is put in use, running, dust'and dirt in time, will cause the brushes to Wear into the surface and form grooves. Sometimes also, sparking occurs and often pi'ts the surface badly. No matter What the cause, a=rough and uneven running contact surface ofa dynamo-electric machine interferes with'proper functioning of the machine and it becomes necessary to overhaul it andto refinish-the contact surfaces.

Refinishing such cont-act surfaces-usually consists in grinding or machin ng the commutator or rings preferably while the dy- '-namo-electric"machine *is operating under running balance although the armature or other part to which the commutator or rings may be attached may be mounted between centers on a lathe and the irregular surface machined or ground down as desired.

Whether the surface be ground or machined the cutting is first rough to expedite thejob, but thereafter the surface is ground with abrasive (usually in block form) of increasing fineness until the surface is'a s smooth as completed for it must be polished :since a smooth glossly surface is most desirable for a for use; :1

stone. hardness.

Application-filed February 23, 1927. Serial' No. 170,411.

run the machine" Without load until the brushes have polished the surface by; long continued rubbing thereon, although if careful'attendance is given to the machine this operation may be done while the machine is in'service. The proper conditionof the sur-- face, that is, the time when it is completely. polished, is usually denoted'by a darkened,-

somewh'at steel blue o'r'chocolate brown appearanceof'th'esurface and the operation requires a comparatively long time depending upon the area of thesurface to be polished, the quality and character of the copper and other factors. I

I have discovered that the finishing and polishingoperations may be expedited'rand an apparently much harder and more lasting surface may-be obtained by addingaquam tity of sulphur to the abrasive usedafor. the last one of thelastgrinding operations. This results in immediately producing.afvery hard, smooth and highly. polished surface eiiceedinglyuresistant to wear:

Preferably finely powdered sulphur from a very small percentage, say oneshalf' of one per cent ,to'any reasonable high percentage, say sixty-fiveper cent, more or less, allby weight, is mixed-with the abrasive mixture before the latter is preparedinxbrickor block form, so that'the sulphuris thoroughly disseminated through or dispersed witlriand among the abrasive particles. The mixture necessary to' bind the whole together. in" a is then putint-otheshape or shapes desired and baked .at such. temperature as' ma v"be.

hard coherent and substantially. homogenenus mass."v The. resulting productcis'ready One way of preparinga grinding block or stone of thischaracter; and the way I now consider preferable,- is to mixabout 20% of sulphur With about80% of fine'abrasi've particles and heat-the mass to a point where the sulphur melts. While the mass remains plast c 'it' is molded to the form and shape desired and allowed togcooll Resins and gums' like shellac may beadded toyield. ahard andtough product andrnot only may'ithe proportion of sulphur be varied but the p kinds and.quantities-of abrasiverparticles canbe obtained. But the surface is-not yet and gums also may be varied. asrequired for manufacturing .tions andv for suchereason, and, depending conditions "and degrees of upon the degree of roughness or fineness of the preceding cut and other factors, the abrasive particles with which the sulphur is mixed are of suitably lesser size. The degree of fineness of the abrasive must'be determined in almost every case by the workman.

In carrying out the process the dynamoelectric machine is started and the preliminary trueing cuts are made. Thereafter the finishing block of abrasive containing the sulphur is applied to the surface and held thereagainst until the whole surface takes on a steel-blue or darkened appearance at which time it should be found to be highly burnished, exceedingly smooth and resistant to abrasive action or wear. This finisiing ,or polishingis accomplished almost instan taneously and the step does not vary from the ordinary grinding with an abrasive block so far as the mechanical action taken by the worker is concerned and may be done in any of the usual manners. It is a novel and in teresting fact, however, that when sulphur is mixed with the abrasive. a. coarser abrasive grain may be used to produce a very smooth and highly polished surface than would ordinarily be used fora finishing cut or grinding of the surface to be polished, and as is not the case with'the latter,no further polishing or rubbing is necessary to produce the steel-blue or slightly iridescent surface.

I do not know definitely whether or not the sulphur in. the abrasive enters into chemical combination with the copper or copper alloy, although it may do so. It is my theory that the heat generated by friction of the abrasive block containing the sulphur causes some of 'the sulphur to combine chemically with the copper with the formation of cupric sulphide (Cu. S.) which the commutator or other copper element nearly resembles in color and appearance after treating,

, or with other metals to. form sulphur compounds therewith, since it is reasonable to assume'that some actionsor reactions may "take place. At any rate and re ardless of theory the effect is to so harden a surface of a copper, copper alloy or other metal article to which it is applied as to make it extremely hard and resistant to abrasion as well as to impart to it a very highpolish. For instance, after polishing a copper commutator in accordance with the invention as disclosed, I have attempted to recut the surface so polished and finished with a very coarse abrasive stone the composition of which was mainly pure silicon carbide, but I found that unusual force and a very great length oftime were required to break through the hard finish previously made by the sulphur stone While'I havedisclosed theinvention in one of its preferred forms it will be appreciated that many modifications and variations surface and cause the sulphur of said composition to unite with the metal of said surface whereby a hardened exterior is formed on said surface.

2. The method of polishing and hardening the contact surface of a commutator which consists in rapidly rotatingthe commutator, and causing the surface of a composition block, including an abradant and sulphur, to

contact the traveling surface of said commutator with sufficient pressure to produce a sulphur compound deposit upon the'surface so treated.

3. The method of polishing and hardening the contact surface of a commutator which consists in rotatingthe commutator to be treated, and urging against-the traveling perimeter of said commutator with sufficient pressure .to generate a substantial degree of heat, a surface of a composition block including sulphur and an abrasive material, whereby a hard composite coating is produced'upon the perimeter of said commutator.

4. The method of'polishing and hardening the cuprous contact surface of a commutator-which consists inrapidly rotating the commutator and subjecting the revolving surface thereof to the action of a relatively stationarily disposed block including an abrasive mixed with sulphur. whereby said surface so contacted is simultaneously polished and provided with a hard copper. sulphur compound coat.

5. An abrasive block for polishing and oxidizing commutators comprising an intimate mixture of abrasivematerial and sulphur, shaped to form a coherent and substantially homogeneous block adapted to be held against the'surface of a revolving commutator whereby said surface is simultaneously polished and a hard composite coating produced thereon.

6. The steps 1n a method of polishing com-, mutators, collector rings and other artlcles containing copper in predominant proportions comprising, SUbJGCtlIlg the surface to applying free sulphurthereto. I

In witnessof the foregoing I affix my signature. j r

WILLIAM i.) WEBER.

be polished to friction and simultaneously 

